SRAC Publication No. 183

August 2001 VI Revised PR

Processing Channel Catfish

Juan L. Silva1,2, Gale R. Ammerman1, and Stuart Dean 2

Catfish of the proper size are sold flow diagrams, and photos of the Receiving and stunning iced, frozen, or battered and bread- main steps in processing catfish Before they are purchased for pro- ed in the following forms: whole; into refrigerated (Fig.1) or frozen cessing, fish are evaluated for unde- dressed (deheaded, eviscerated and (Fig. 2) products are described in sirable characteristics such as over- skinned); filleted; steaked; or as this publication. strips or nuggets. Size control of fil- all appearance and off-flavors by lets to within 1- to 2-ounce weight experienced “taste increments is essential in marketing Live Whole Fish testers.” Sample fish are the filleted product. Fish of the taken from the pond at appropriate size that will yield the Vats least three times: two number of fillets needed are weeks before harvest, processed by hand at filleting tables Stunning the day before harvest, or by automatic filleting machines. and the day of harvest. If any fish sample is The fillets are trimmed to yield the Automated Lines Manual Line(s) nugget and the shank fillet, then deemed unsatisfactory, sized and either frozen or packed in fish from that pond will ice for shipment. Channel catfish Deheader Band Saw not be accepted until the “steaks” are prepared by cutting condition improves. Fish large fish into cross-section pieces. are loaded into aerated The steaks are then individually Filleter Cavity Cut water tanks and trans- quick frozen (IQF) or packed in ice. ported from the pond to the processing facility. Other products are derived from Skinner Eviscerate these primary cuts. The fish are unloaded from the truck into bas- In order to make various product nugget Trim Skinning kets for weighing and forms, several steps must be com- then placed in an aerat- pleted in processing channel catfish ed holding vat or direct- (Ictalurus punctatus) into a mar- Sizing Chill ly onto a conveyor belt ketable product. These include whole dressed to the plant. In most receiving and weighing the live fish fish cases, fish enter the pro- at the processing plant; holding Chill Sizing cessing line directly them alive until needed; then stun- from the trucks and are ning, deheading, eviscerating, skin- kept in holding vats ning, chilling, size grading, freezing Ice Ice only long enough to sus- or ice packing, packaging, ware- tain plant operation if housing, icing, and shipping the fin- fish delivery is delayed Cooler ished product. Brief descriptions, Cooler (Fig. 3). The fish are placed in cages or car- ried on a belt that passes 1 A A Department of Food Science and under electrodes where Technology, Mississippi State University they are stunned with an 2 Figure 1. Flow diagram for processing ice-packed Food and Fiber Center, Mississippi State electrical current for a University channel catfish fillets (manual and automatic). few seconds. This makes them easi- From Cooler/Process er and safer to handle by workers (Fig. 4). The fish are moved into the A processing plant on a distribution conveyor belt (Fig. 5). The dressing area is divided from the receiving area (outside) by a wall. The fish are conveyed and manually or auto- matically size graded for each fillet- ing operation. Fish other than cat- Vacuum Tumble Ship Ice Pack Bread & Batter fish (sometimes called “trash fish”) or are sometimes present in ponds and Injection may be inadvertently harvested with the catfish. These fish are dis- Heat Set Bread carded at this point. Oversized fish (fish larger than what can be han- IQF dled by automatic filleting lines) are sent to the manual draining/fillet- IQF ing line for processing. Water Glaze Manual dressing Deheading Pack From the distribution conveyor belt, the stunned catfish drop into a holding bin for each processing line. Freezer In general, fish are sorted into each line automatically (by weight) or manually to attain maximum yield and efficiency in the automated Ship lines. The first line operator is the lay-up person, who positions each Figure 2. Flow diagram for processing frozen channel catfish fillets. catfish for quick and efficient head removal by the bandsaw operator (Fig. 6). The head is pushed into a chute that routes it to a waste dis- posal conveyor belt below the band saw, and the carcass proceeds to the evisceration operation. A good band saw operator can process 40 to 50 fish per minute.

Evisceration The body cavity is opened by hand with a knife, and viscera are with- drawn through a suction tube (vac- uum eviscerator) (Fig. 7). One deheader will feed about six evis- ceration stations. Viscera are con- veyed to the offal collector, and the eviscerated carcass proceeds to the skinning operation.

Skinning The membrane skinner has been the standard industry machine for skin- Figure 3. Fish are held in holding tanks (vats) before processing. ning channel catfish since its intro- duction. This machine has a rotat- ing roller with sharp “teeth” that present the fish to a sharp blade held in place by spring pressure lost before packaging. It is extreme- ly important to control the micro- bial build-up in the chiller water, because this is directly related to the safety and shelf-life of the fish. Because chiller water is usually not changed until the end of the day, a turnover rate of about 1 gallon of water per 5 pounds of fish is rec- ommended. Some processors add up to 20 parts per million of chlo- rine to the chiller water or rinse water. Water is added continuously to replace water uptake. Fat is also skimmed off. Some processors place this step before the skinning operation and after the evisceration station.

Size grading When fish leave the chill tank they are conveyed into a grading or a Figure 4. Fish are electrically stunned before processing. sizing station. Here they are sorted by weight. In small plants, grading (Fig. 8). Very close tolerances located underneath the skin. may be a hand operation; in larger between the blade and roller teeth Capacity is about 12 to 14 fish per plants, mechanical or electronic siz- make it possible to remove only the minute per operator. Most proces- ing systems are used. These use a skin as the fish is passed over the sors use two operators per machine, photoelectric cell (a scale which roller. This tolerance is important in so the machine capacity is 24 to 28 weighs the fish and sends an elec- determining yield and fat content of fish per minute. tronic signal) to send a signal to the the final product, since most fat is correct “station/ gate” to open and Chilling let the fish out when it passes After deheading, evis- through (Fig. 10). These graders cerating and skinning, usually size fish in 2-ounce inter- the whole dressed fish vals. These fish are then ice-packed, is lightly spray-washed injected and frozen, or further and conveyed into the processed as explained later. chill tank where it is immersed in a mixture Automatic filleting of ice and water, or o The stunned fish are manually sort- cold water (≤35 F) ed by size or automatically sorted refrigerated indirectly by weight as described earlier. with ammonia. Depending on the number of auto- Chilling is the process matic lines, whole fish are sorted in of lowering the temper- different size/weight ranges so as ature of the fish by to attain maximum yield and pro- immersing them in ductivity. Each filleting line can cold water for a set process up to 60 fish (120 fillets) per period of time. Fish are minute. The fish are then placed held in the chill tank vertically (or horizontally in some for 10 to 30 minutes, deheaders) with the head up on an depending on size, at a o automatic deheader (Fig. 11). This temperature of 38 F or is a rotating machine with several less (Fig. 9). Fish must knives that cut off the head and be cooled rapidly and o pull most of the viscera with it. The held below 40 F to deheaded fish, with some remain- attain low microbial ing viscera, are dropped onto a load, good flavor, and holding table. The head and viscera maximum shelf-life, are sent to an offal room. Fish from and to ensure overall the holding table are taken individ- quality. Fish may gain ually by an operator and positioned up to 1 percent weight onto guides (head first) to be fillet- Figure 5. Distribution belt from stunning to primary by water absorption at ed. The filleting machine has two processing. this point, but most is lets are sorted in 2-ounce incre- ments from less than 3 ounces to more than 17 ounces. Fillets for fresh market are dropped in tagged boxes with a plastic liner and iced to a 1:2 fish to ice ratio by weight. The remainder are placed on tagged plastic totes and held in a cooler until frozen or otherwise processed.

Freezing Before freezing, channel catfish products are treated (injected or tumbled) with a polyphosphate solution that acts as an antioxidant and prevents excessive water loss during freezing. The most important part of main- taining excellent quality frozen fish Figure 6. Deheading operation with a band saw (manual). is ensuring that they are processed and frozen rapidly, and held at 0 oF or below until used (Fig. 2). The temperature at the core of the fish must be reduced from 32 to 15 oF in 30 minutes or less for the fish to be considered quick-frozen, and for it to retain its original quality. Surface freezing alone is not sufficient because the fish will thaw in stor- age before refreezing, which leads to textural breakdown, oxidation and shorter shelf-life. The channel catfish are IQF (Fig. 14) in a cryo- genic tunnel or mechanical spiral freezer. Carbon dioxide, liquid nitrogen, or conventional mechani- cal (ammonia) freezing systems are being used in various plants to freeze channel catfish. The choice of freezing media and machinery is mainly a question of economics. Depending on the source, produc- tion rates of more than 2,000 Figure 7. Evisceration (vacuum) stations to remove viscera manually before skin- pounds per hour are handled by ning. mechanical freezing. The fish or fish pieces are evenly distributed rotating knives in series that cut the manually with a filleting knife to manually on the conveyor belt to fillets from the frame (Fig. 12). The separate the nugget and bones from the freezer. The variable speed belt fillets drop skin down onto a con- the finished fillet, called the is regulated so that the fish remain veyor belt, while the frame and “shank” (boneless) fillet (Fig. 13). in the freezing chamber for the remaining viscera drop onto the Trimmers are sometimes paid by required time and are completely offal line. These are carried to the production and yield, by weighing frozen when they exit the tunnel. offal station by a conveyor belt, fillets in and shank fillets, nuggets water flumes or vacuum. The fillets and trimmings out. This is a labor- Packaging are conveyed to the skinner where intensive operation, requiring 12 to Frozen they are pressed against two rotat- 16 trimmers per filleting line. The ing knives that remove the skin. shank fillets are then placed on a When whole frozen fish leave the The fillets are sprayed with water conveyor belt, cooled in a rotating freezer, they are conveyed through that may contain up to 50 ppm chiller with ice water or refrigerat- a water bath or sprayer. A coating total chlorine to reduce bacterial ed water and conveyed to the grad- of ice (glaze) is formed over the load; then they are conveyed to the ing station. Here they are sorted fish. This is the first step in packag- trimming table. Fillets are trimmed automatically by weight. Shank fil- ing. The IQF, glazed, whole fish or fillets are sized and packaged in cardboard shipping cases lined with polyethylene bags. The whole frozen fish are divided by weight (in 2-ounce increments) and packed in 15-pound boxes. Frozen fillets are packed in 15-pound boxes, with fil- lets divided into lots within a 1- to 2-ounce range (Fig. 15). They are weighed and may pass through a metal detector (a critical control point in HACCP plans) before warehousing and shipping.

Ice-packed Whole iced fish are divided into the same size categories as whole frozen fish and packed in ice in 50- pound shipping boxes that contain 30 pounds of fish and 20 pounds of ice. Steaks are packed in 15-pound Figure 8. Mechanical skinning operation of whole fish. shipping cartons. Warehousing Frozen channel catfish are held at 0 oF (or below if required by state law) in a frozen storage warehouse until shipped. The iced product is usually packed and shipped within 48 hours in refrigerated trucks. It is held at the processing plant in refrigerated storage at 30 to 38 oF until shipped. Recent developments and new technologies The catfish processing industry is still very young. It has evolved from a mostly manual batch opera- tion into a semi-automatic, semi- continuous operation. This has led Figure 9. Channel catfish in a chill tank. to increased production and quality. However, there is much room for improvement in productivity, effi- ciency and yield, quality and chill life, and safety. One of the advan- tages of catfish is the freshness of the product. Theoretically, a fish may enter the plant and be ready for distribution in 2 to 4 hours. Catfish also can have a long shelf life. However, there are still prob- lems with manual trimming, lower- ing temperature quickly, handling, and product flow. Some innovative technologies are becoming available to increase production, yield, quali- ty, and safety of the product. One system recently developed takes the fish, after receiving and stunning, into a hopper feeding Figure 10. Automatic size graders used for dressed and filleted catfish. deheader/eviscerator unit that removes most of the viscera, the pelvic fins, and head. A secondary evisceration system removes the remaining viscera and most of the tail fin. This primary process could be segregated from the filleting process. The fish is then conveyed to an air-agitated, counter-flow, two-stage chiller. The prechiller cleans and removes most of the blood, while the chiller cools the headed and gutted product. This is then placed in a filleting machine that removes the dorsal bone. The fillets are then sent to a trimming line (less trimming needed) and on to icing/grading or other processes. The resulting frame also yields a better quality mince (less blood and viscera). This process is designed to flow better, produce a better quality Figure 11. Automatic deheading station. product, and perhaps lower the incidence of bacteria. The rapid cooling and better eviscerating improve filleting and trimming processes, yield and quality. Another technology combines machine vision with a cutting-edge (water pressure) to produce uni- formly cut strips and other prod- ucts. The fillet is presented to a camera that processes the image and sends a signal to the cutter to produce the most efficient, uniform cut. Processes such as prechilling fish before processing have been attempted. However, catfish are subtropical/temperate fish, and if chilled immediately after harvest or receiving, may produce a pink, soft and exudative muscle. Figure 12. Automatic filleting machine. Grading and quality control soft- ware and hardware are now avail- able from many vendors. This tech- nology allows the production and quality assurance departments to follow operations continuously and make adjustments rapidly. Such software also can be used to moni- tor critical control points in a Hazard Analysis and Critical Control Points (HACCP) system. Requirements and regulations Federal, state, local and, if export- ing, international regulations must be followed from the design to the production stages. These regula- tions cover Good Manufacturing Figure 13. Manual trimming of fillets from automated lines. Practices, GMPs (Title 21, Code of Federal Regulations, part 110, www.fda.org), as well as environ- mental and occupational safety. Some of the agencies that oversee catfish processing operations are the U.S. Food and Drug Administration (FDA); the Environmental Protection Agency (EPA) and its state equivalent; state health and/or agriculture depart- ments; the Occupational Safety and Health Administration (OSHA); and others. Recent regulations require seafood processing plants to conduct a hazard analysis and implement a Hazard Analysis and Critical Control Points (HACCP) plan (Title 23, Code of Federal Regulations, part 123, www.fda.org), including Sanitation Standard Operating Procedures (SSOPs). Figure 14. Fillets are individually quick frozen (IQF), glazed and packaged.

Figure 15. Frozen fillets are placed in plastic-lined boxes, weighed, and passed through a metal detector (if needed). This publication was supported in part by a USDA-CSREES Grant No. 98-38500-5865 from the United States Department of Agriculture, Southern Aquaculture Center. Publication is an update of SRAC Publication No. 183 by Gale R. Ammerman.